This invention relates to the field of mass storage devices. More particularly, this invention relates to unlatching the actuator of a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding and decoding data so that it can be successfully written and retrieved from the disc recording surface. A microprocessor controls most of the operations of the disc drive as well as passing the data and commands between a host computer and the disc drive.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) that includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air-bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring that produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage disc after the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided into sectors. The sectors are grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
When power to the actuator is not present, it is moved to a safe location on the disc, or xe2x80x9cparked.xe2x80x9d Many times a magnetic latch is employed to hold the actuator in the parked position. When the actuator must be moved from the parked position, current disc drives progressively pump or step-increment current to a voice coil motor (VCM) coupled to the actuator, until the actuator produces a force to break the magnetic force used to latch the actuator. After overcoming the magnetic force, movement of the actuator is monitored closely by the servo controller to prevent the actuator from hitting a crash stop generally positioned at the outer periphery of the disc.
Due mainly to the increasing popularity of portable and notebook computers, there is a trend in the industry towards increased non-operating rotational shock requirements. This in turn requires magnetic latches to have greater capacity. In other words the magnetic latch must apply larger amounts of magnetic force. The prior art approaches to unlatching an actuator require an incremental step of current to be provided to the VCM to unlatch the actuator; this method is also known as DC unlatch. For a larger magnetic latch, using this method, a large amount of current will be needed to pump to the VCM. The amount of current necessary to employ the DC unlatch method is a primary factor in increasing the size and cost of the power amplifier required to produce such a current. There is a strong desire in the industry to reduce the size and cost of disc drives, rather than increase them. Therefore, the DC unlatch method is unacceptable for disc drives intended to have increased non-operational rotational shock requirements.
Another approach is a method called AC unlatch. In this method, the current to the VCM is applied in an alternating direction so as to produce a resonance frequency equal to the natural frequency of the bumper that holds the magnetic latch.
There are various prior art schemes for monitoring the movement of the actuator. For example, back EMF of the VCM, or grey code information, may be used to indicate the acceleration or velocity of the actuator.
An information handling system, such as a disc drive, comprises a base, an actuator attached to the base, a voice coil motor, and a disc stack rotatably attached to the base. The voice coil motor determines the motion and position of the actuator. The disc is divided into a plurality of servo zones, corresponding to a respective plurality of profiles of the actuator motion with respect to the disc. A current driver applies variable magnitude current to the voice coil motor, based on the particular servo zone where the actuator is located. The disc may be provided with at least a parking band zone defining a first area in which the actuator remains parked, and a guard band zone defining a second area in which the actuator has just become unlatched. The parking band zone may be provided with a servo system that determines whether the actuator has unlatched successfully. The current driver may apply alternating current when the actuator is in the parking band zone. The servo system may monitor the position of the actuator when the actuator is in the guard band zone, and the controller may control the current driver to adjust the speed of the actuator based on the motion of the actuator. The current driver may apply at least two, and preferably four, different frequencies of alternating current while the actuator is latched. The current driver may attempt to unlatch the actuator at least two, and preferably thirty-two, times. The current driver may change the frequency if at least one, and preferably eight, attempt(s) has (have) been unsuccessful. The current driver may apply a variable initial current magnitude during each subsequent attempt to unlatch the actuator after an unsuccessful attempt. The invention includes a method of accomplishing any or all of the functions of such an information handling system or disc drive.
Advantageously, the invention reduces the amount of current necessary to unlatch the actuator. Therefore, the invention decreases the size and cost of the power amplifier required to produce an unlatch current. Advantageously, this invention is well suited for disc drives intended to have increased non-operational rotational shock requirements.